Plastic injection molding machine melt the plastic granules and set them in a mold to give a defined shape. They can be of different categories and sizes with specific features and benefits. Using these devices, you can manufacture any kind of plastic components, including parts of mobile, laptops, vehicles, utilities, toys, and all plastic commodities of daily use.
In this guide, we brought you an in-depth discussion on plastic injection molding machines to let you know the ins and outs. You will also find some top-notch recommendations for your project. So, without any further delay, let’s drive in:
What is a Plastic Injection Molding Machine?
A plastic injection molding machine is a device used to create various plastic products by melting the plastic granules and molding them into different shapes. These machines can be of varying sizes & types with which the manufacturers can design any kind of plastic products like- toys, automobile parts, containers, utensils, electronic gadgets, etc. Every plastic injection molding machine consists of two essential parts-
- Injection unit
- Clamping unit
The plastic is melted and injected into the molds in the injection unit. Then, pressure is applied to the clamping unit to solidify and shape the plastic.
However, the plastic granules inserted in these devices can be Thermoplastics or Thermosetting plastics. Engineering plastics are also used in some cases, such as molding automotive and medical devices.
What Do Plastic Injection Molding Machines Make? – Application
All varieties of plastic parts are molded in plastic injection molding machines. These include- automotive parts, consumer products, medical devices, and other industries like electronics, packaging, etc. Here are some examples of its application:
| Industry | Produced Item |
| Automotive Industry | Instrument panels, air vents, bumpers, grilles, door panels, handles, engine covers, fluid reservoirs, battery housings, seat components, etc. |
| Consumer Goods | Containers, kitchen utensils, toothbrushes, razors, TV casings, remote controls, game consoles, etc. |
| Medical and Pharmaceutical | Syringes, IV components, diagnostic equipment housings, etc. |
| Packaging Industry | Beverage bottles, food containers, lids, caps, cosmetic bottles, etc. |
| Electronics and Electrical | Electrical connectors, plugs, switches, buttons, casings for laptops, mobile phones, circuit board holders, sockets, etc. |
Types of Plastic Injection Molding Machines
Considering the technology used in the injection machine, these devices can be of three types. These are as follows-
Hydraulic Injection Molding Machines:
Hydraulic injection molding machines use a hydraulic system to create the clamping force that holds the mold shut. They consist of pumps, valves, and pistons that use pressurized hydraulic fluid to push molten plastic from the barrel into the mold cavity. Based on the pump, they can be fixed, or variable pumped molding machines.
| Pros | Cons |
| DurableHigh pressureLow initial cost Mass production | Slower Speeds Low preciseness Less energy-efficientMore expensive to runNoisey |
Electric Injection Molding Machines:
Electric injection molding machines use electric motors to initiate the movement of the plastics in the molding process. Each molding stage is controlled by individual electric or servo motors, which bring high precision and accuracy. Besides, unlike Hydraulic injection molding machines, they have fewer moving parts and a less complex system. Thus, electric ones are better than hydraulic machines.
| Pros | Cons |
| Greater controlQuiet operationEnergy-efficientLow-maintenanceIdeal for small and precise moldingsLess prone to malfunction | Not suitable for large parts Need greater technical expertise to operate |
Hybrid Injection Molding Machines:
Hybrid injection molding machines are a combination of electric and hydraulic systems. They use an electric motor for the injection unit and install a servo-hydraulic system for the cramping unit. Thus, preciseness is maintained, providing high-pressure capabilities due to the hybrid structure.
| Pros | Cons |
| Energy efficientGood balance of clamping force and speed | Higher upfront costNot ideal for all applications |
The plastic injection molding is available in two configurations- vertical and horizontal. This indicates the orientation of the clamping unit.
Vertical Injection Molding Machine:
In a vertical injection molding machine, the mold moves on a vertical axis, up and down. The molding mechanism occurs at the top of the mold, ensuring a consistent flow of the molten plastic due to gravity. The vertical injection molding machines are ideal for large production as they can be automated. However, these devices require human assistance or a robotic arm to unmold. They take up less ground space, making them ideal for congested spaces.
| Pros | Cons |
| Space-savingQuick filling time Easy to clean Well-suited for automation | Limited clamping forceNot be suitable for very thick-walled partsRequire additional arms to mold out |
| Pros | Cons |
| Higher clamping forceFall freely out of the mold cavity | Not suitable for automationRequires more space Need complex fixturing to hold molds |
Considering the number of plates to support the mold, plastic injection molding machines have two or three plates. They can be hydraulic, eclectic, or hybrid.
Two-Platen Injection Molding Machine:
The two-platen injection molding machines have two horizontal plates to hold the molds. There is a fixed platen that remains stationary, while the moving platen houses one half of the mold and moves to clamp against the other half. These devices are ideal for small to medium production levels.
| Pros | Cons |
| Compact designAffordableVersatile & flexible | Limited to simpler moldsLess energy-efficient |
Three-Platen Injection Molding Machine:
Three horizontal plates hold the mold in three-platen injection molding machines. The three platens include:
- A fixed platen
- A moving platen
- An ejector platen
The additional platen in these machines offers more flexibility in mold movement and core pulling mechanisms.
| Pros | Cons |
| Handle larger and heavier moldsIdeal for large-scale productionEasy cleaning and maintenance | More expensiveNeed more technical expertise to operate Bulky in size |
How Does a Plastic Injection Molding Machine Work? – Step-by-Step Process
Before understanding the working mechanism of an injection molding machine, you must know the components or parts of this device. A plastic injection molding machine consists of the following parts:
- Hopper
- Heater barrel
- Screw
- Nozzle
- Mold
- Platen (fixed and moving)
- Ejector pins/plates and ejector rods
The orderly coordination of all these parts makes the molding of a plastic injection molding machine successful. Here is the stepwise procedure of the manufacturing process using this device:
Step 1: Material Feeding & Melting
First, input the raw material or the plastic pellets into the machine’s hopper. These are then transferred to the heater barren, where they are melted for molding. A rotary screw is installed inside the heater that mixes the melting plastics and pushes them forward to the molding cavity.
Step 2: Injecting The Molten Plastic Into The Mold
The nozzle or gate between the injection and clamping section closes as the melted plastic reaches the end of the barrel. Pressure is built inside as the screw moves back to draw in a set amount of plastic. This built pressure is called clamp pressure, which closes the mold halves tightly. Maintaining a balance between the injection and clamp pressure is crucial to avoid plastic leaks. Once adequate pressure is created inside the chamber, the screw moves forward, opening the gates, and the molten plastic is transferred into the injection molds.
Step 3: Holding & Cooling
After the plastic injection, the mold is kept under pressure to settle the injected material. This holding time can range from milliseconds to minutes, depending on the plastic type. Once this stage is complete, you need to set the mold for cooling, which can take a few seconds to some minutes. The holding and cooling time duration depends on the size, complexity, and type of plastic used for molding.
Step 4: Ejection and Finishing Processes
Once the plastic inside the mol solidifying is complete, it’s time to unmold it. Ejector plates or pins are used to release the plastic from the mold. Thus, you get the product of your desired shape in your hand. Now, you can give final touches like- removing excess plastic, polishing, or dying.
Factors to Consider In Choosing the Right Plastic Injection Molding Machine
As discussed above, plastic injection molding machines are available in different styles, designs, and sizes. Each of these categories has individual application and production specifications. How about deciding which machine is right for your molding requirements? Here are some facts to consider to pick the right one:
Machine Size and Footprint
Considering the machine’s size is crucial to ensure the device fits in your space. For small areas, vertical injection molding machines work best. They have a smaller footprint compared to horizontal machines. Thus, you can save ground space using vertical machines. Besides, some portable desktop injection molding machines are also available that are small in size. However, these mini devices are only suitable for small scaling.
Clamping Force
The clamping force ensures the mold remains wholly sealed, preventing plastic leakage. The ideal clamping force varies depending on the size, wall thickness, complexity of the produced parts, and the type of machine you use. You can find the required clamping force for your plastic injection molding machine using this formula:
| Clamping Force (tons)=Projected Area (square inches)×Tonnage Factor |
NB: The tonnage factor typically ranges from 2 to 5 tons per square inch, depending on the material.
Here is a chart suggesting clamping force for various applications to help you pick the suitable plastic injection molding machine:
| Industry | Clamping Force Range | Products |
| Automotive | High clamping forces (500-2000+ tons) | Large and complex parts like bumpers and dashboards |
| Consumer Electronics | Medium clamping forces (150-500 tons) | Detailed and high-precision parts like housings and connectors |
| Medical Devices | Small and medium clamping forces (20-300 tons) | Precise and sterile components |
| Packaging | Medium to large clamping forces (200-1000 tons) | Bottle caps and containers |
Type Of Plastic To Use
Different plastic injection molding machines have varying plastic preferences based on the injection molding process. Some machines are suitable for thermoplastics, while others may prefer thermosetting plastics as raw material. So, you must consider what product type you manufacture and select the correct machine accordingly. Below, we are adding a chart to help you find the suitable device based on the type of plastic use:
| Plastic Injection Molding Machine | Suitable Plastic Material |
| Hydraulic Injection Molding Machines | Polypropylene (PP)Polyethylene (PE)Polyvinyl Chloride (PVC)Acrylonitrile Butadiene Styrene (ABS) |
| Electric Injection Molding Machines | Polycarbonate (PC)Polyamide (Nylon)Polystyrene (PS)Polyethylene Terephthalate (PET) |
| Hybrid Injection Molding Machines | Polyoxymethylene (POM or Acetal)Thermoplastic Polyurethane (TPU)Polyether Ether Ketone (PEEK) |
| Two-Shot (Multi-Shot) Injection Molding Machines | Combination of PP and TPE (Thermoplastic Elastomer)ABS and PC |
| Vertical Injection Molding Machines | Polycarbonate (PC)Polypropylene (PP) |
| Micro Injection Molding Machines | Polylactic Acid (PLA)Polyethylene Terephthalate (PETG) |
| High-Performance Plastics and Specialized Machines | Polysulfone (PSU)Polyimides |
Production Volume
Production volume refers to the number of product molds in a given time frame. You must consider the production volume to ensure the machine you purchase can meet your daily or monthly production requirements. Usually, hydraulic injection molding machines are suitable for medium to high-scale production. And for small to medium-scale volumes, you can go for the electric ones.
Cycle Time
Cycle time is the total duration required to complete one molding process, which includes injection, cooling, and ejection. Low cycle time means faster production. This duration differs for the size and product you manufacture and the variant of machine you use. For instance, hydraulic injection molding machines usually have 30 to 120 seconds cycle time. The cycle time of electric injection molding machines ranges from 10 to 30 seconds. That is, these devices have more speed compared to the hydraulic ones.
Additional Features
For advanced performance, you should consider some additional features, such as:
- Consider features like closed-loop control, real-time monitoring, and predictive maintenance to optimize the performance.
- Robotic integration and automation
- Consider high-capacity water channels or temperature control units for an efficient mold cooling system.
- Look for safety measures like interlocks, guards, emergency stop buttons, and safety PLCs (Programmable Logic Controllers).
- Remote monitoring and controlling facility
Energy Efficiency and Budget
Electric and hybrid machines are more energy efficient than hydraulic ones. They often come with advanced energy-saving features like servo-driven systems and regenerative braking. Though these increase the initial investment cost, they are cost-saving in the long run. In contrast, although they are less expensive, hydraulic machines tend to consume more energy. Thus, they need high maintenance costs.
Maintenance Tips For Plastic Injection Molding Machine
You must take care of the plastic injection molding machine to ensure it lasts longer. Here are some essential maintenance tips to follow:
Regular cleaning:
Dust accumulation in the molds can damage the produced items. So, clean the molding machine and its surroundings regularly. However, make sure to turn the device off while cleaning it.
Lubrication
When the plastic injection molding machines run long, they may lose their smoothness. Lubricating the moving parts of the machine is helpful in this case. You should apply lubricants on the mold, screw, barrel, and other parts that you find jamming.
Inspection
Inspect the machine to look for any damage or broken parts. You should also look for leakage issues and ensure the clamping force is accurate. Further consider the type of injection molding to examine properly. If you find any broken parts, repair or replace them ASAP.
Check Electrical & Operations
Keep the electrical components, like the wiring and controlling system, in check. Besides, don’t overload the machine. Set the device according to the manufacturer’s recommendations. to ensure accurate and consistent production.
Train The Machine Operators
Train the machine operators on how to use the device. Let them know about the correct clamping force, duration of operation, and safety procedures.
Troubleshooting Common Issues Of Plastic Injection Molding Machine
Like other devices, plastic injection molding matches face some issues while operating. Here are the most common ones that you must know before using these devices:
Short Shots:
Short shots are the most common phenomenon in a plastic injection molding machine, where the molds are partially filled. Too low temperature and injection pressure are the cause of such occurrences. Besides, uneven plastic pellets and insufficient liquidity can result in short shots.
Solutions:
- Increase the injection speed
- Check if the valve and the inner wall of the material are fine
- Increase the temperature to liquefy the material
Burn Marks:
Burn marks may be visible near the venting area or on the molded parts. This can be caused due to excessive melting temperature, high-speed injection, or if the screw rotation speed is too high. Besides, holding the mold longer and not letting the gas out in time can cause burn marks, too.
Solution:
- Reduce melting temperature
- Adjust injection speed
- Optimize screw rotation speed
- Ensure adequate venting
Flash:
Flash refers to the excessive plastic accumulation on the finished products. This occurs due to a defect in the mold, excess material, insufficient clamping force, or inappropriate exhaust system. Here are the remedies to this problem:
Solution:
- Ensure the mold is of accurate size and has no leakage
- Increase the injection time
- Reduce the injection speed and pressure
Jetting:
Jetting refers to the spray marks on the plastic injection molding machine caused by the overflow of the molten plastic. This is due to excessive injection speed or the gate being too small.
Solution:
- Reduce the injection speed
- Install a submarine or overlap gate
- Increase the flow channel’s width
Voids:
While molding, thick parts, vacuums, or voids may be noticed on the mold product. It happens when the temperature is not cool enough while solidifying. As a result, the cooling plastic melt shrinks towards the mold walls, creating a vacuum void inside the molded part.
Solution:
- Reduce melt and mold temperature
- Reduce injection speed
- Increase holding pressures & time
- Increase pack pressure and time
Besides these, plastic injection molding machines can face many other issues like- delamination, air traps, flow line marks, streaks, sink marks, etc. You should regularly maintain the machine to avoid such problems.
The Bottom Line
Plastic injection molding machines are used to manufacture various plastic products. In choosing the ideal device for your project, you must look after the product category, production volume, factory size, budget, etc. Considering all these factors, decide what machine you need: hydraulic, electric, or hybrid.
The suggested companies in this guide will be your best choice as they are 100% reliable. However, target Chinese companies if you want a high-quality yet affordable product. This will bring you a customization facility along with global shipment. Besides, prioritize production cost, automation, advanced controlling, and IoT features to pick the best one.
FAQs On Plastic Injection Molding Machine
What is the cost of a plastic injection molding machine?
Depending on the size and type, plastic injection molding machines usually range from US $2000 to $500000.
How long does the injection molding process take?
The whole injection molding process may take approximately 10 to 120 seconds. This duration depends on the size and complexity of parts and the machine’s features.
Can recycled plastics be used in a plastic injection molding machine?
You can use recycled plastic in a plastic injection molding machine as raw material. They are as durable as the fresh plastic granules.
What are the components of a Plastic Injection Molding Machine?
A plastic injection molding machine’s main components include an injection unit, clamping unit, mold, and a control panel.
Can one injection molding machine produce three products?
Yes, one injection molding machine can produce three or more products depending on mold type. Multi-cavity molds, stack molds, indexing molds, and multi-component molds are suitable options for this purpose.
Can the injection molding machine work 24 hours a day?
Yes, the plastic injection molding machines can work 24 hours a day, but you must ensure proper maintenance and avoid overloading the device.
What is the L/D ratio of an injection molding machine?
The L/D stands for length-to-diameter. It indicates the molding machine’s ratio of the length of the screw to its diameter.
How often should a plastic injection molding machine be replaced?
The replacement of a plastic molding machine depends on its maintenance. A low-maintenance machine may require frequent replacement. However, devices set for high-volume production are best replaced after 7 to 10 years.
